The present invention relates to tape drives, and more particularly the present invention relates to a linear digital tape drive having a backward-compatible auxiliary head and head positioning assembly enabling read back of outdated standard tape formats.
Magnetic tape is widely used for recording digital information. One extensive use of digital tape recording is to provide backup and archival storage of vast quantities of digital information, such as records comprising blocks of data. In some applications archival records are recorded on tape in a particular tape format which follows agreed standards at the time the recording was made. The tape may then be placed into archival storage and not retrieved until months or years have passed by. It is not uncommon to specify the useful storage life of recorded digital tapes and cartridges at thirty years, or longer. Whatever may be the useful life of a particular magnetic tapes, a primary assumption on the part of those who store such tapes away is that the recorded information may be read at some date in the future, if access to the archived data is required.
While a particular tape and cartridge may remain functional over many years after being in archival storage, tape transport mechanisms typically do not last nearly so long. Standardized tape recording formats are also susceptible to evolutionary changes and improvements. These changes are primarily driven by improvements in magnetic tape and magnetic head technologies which enable much larger data records and files to be stored on a given area of magnetic tape. One recent development, first employed in the hard disk drive industry, and more recently applied to tape recording, has been the introduction of head assemblies formed of thin film inductive, and magneto-resistive, and giant magneto-resistive (MR) read elements. These elements are typically fabricated in processes including photolithographic patterning steps of the type first developed for use by the semiconductor industry. One desirable aspect of these new thin film MR heads is that head gap widths may be narrowed considerably. Narrower head gaps and finer grain magnetic media coatings on tape mean that many more lineal data tracks may be defined across a magnetic recording tape of a standard given width (such as one-half inch tape). Also, the head structure may be formed as a single small composite structure on a common base or substrate and have as many as 12, or more, distinct heads. By using a common substrate, the heads may be formed to be in a predetermined precise alignment relative to nominal track locations defined along the magnetic tape. With e.g. 12 write and read head elements of the head structure in precise alignment with the defined nominal track locations, and with large scale integrated chips providing multiple data write/read channels, it has now become practical to have e.g. 12 channels for simultaneously writing user data to tape and for reading user data back from tape. This increase in the number of write/read channels effectively increases the overall data transfer rate between a host computer and the tape drive, and enables the tape drive to be characterized as having higher performance than previously available.
In order to take full advantage of the new thin film MR head technology in tape drives, a track layout which differs from previous standard track formats is required. This new track layout employs tracks of much narrower track width and pitch. Since the write/read heads are grouped together on a common fabrication substrate, the data tracks are also grouped together. In one arrangement, the data tracks are grouped into bands, or zones, across the tape, such that e.g. ten lateral head positions relative to the tape within a single zone would access 120 tracks. When a zone boundary is reached, the head structure or assembly is then displaced laterally relative to the tape travel path to the next zone, and the tracks of that zone then become accessible. Because track widths are very narrow, enabling track densities of e.g. 2000 tracks per inch, or higher, lateral tape motion must be followed in order to keep the new head assemblies in alignment with the tracks during tape travel past the head. Magnetic servo patterns written onto the tape may be read by servo readers and used to generate position error signals used by a closed loop positioner to correct head position. Alternatively, optical servo patterns embossed or otherwise formed on a back side of the tape may be used to provide position error signals, as disclosed for example in commonly assigned, co-pending U.S. patent application Ser. No. 09/046,723 filed on Mar. 24, 1998, and entitled: xe2x80x9cMulti-Channel Magnetic Tape System Having Optical Tracking Servoxe2x80x9d, the disclosure thereof being incorporated herein by reference.
The later high-density track format differs from previous standard formats. For example, FIG. 1 shows an existing standard tape format employing longitudinal recording. In this example a magnetic recording tape 10 has a series of parallel longitudinal tracks. Three tracks 12A, 12B and 12C are shown in the FIG. 1 example, although more tracks, such as 24, 48, 96 or 128 tracks may be employed in a one-half inch tape lineal format in accordance with a particular standardized track layout plan. A head assembly 14 includes e.g. discrete inductive read or write head elements 14A, 14B and 14C which are aligned with the tracks 12A, 12B and 12C. Other tracks may be accessed by displacing the head assembly 14 laterally relative to the direction of the tape along a path indicated by the vertical arrows axial aligned with the head 14 in the FIG. 1 view.
Another preexisting standard tape format employs azimuth recording of the data tracks, i.e. adjacent tracks are recorded with magnetic gaps oblique to each other, creating what appears generally as a xe2x80x9cherringbonexe2x80x9d pattern, shown in FIG. 2. Therein, one track 16A has its magnetic flux reversal pattern aligned with a first azimuth angle oblique to the tape travel direction, and an adjacent track 16B has its magnetic flux reversal pattern aligned with a second azimuth angle in an opposite sense of the first angle relative to a travel path of the magnetic tape 10. One known advantage derived from azimuth recording is that lineal guard bands or regions between tracks may be reduced, and the tracks may be placed closer together and read back without interference from adjacent tracks. While azimuth recording technology increases track density somewhat, complications arise in writing and reading the slanted tracks. Multi-element tape heads, such as the tape head 100 shown in FIGS. 4-6 of U.S. Pat. No. 5,452,152, can be provided with some of the write/read elements having magnetic gaps aligned with one azimuth angle, and other write/read elements having magnetic gaps aligned with the other azimuth angle. Such heads are then positioned laterally relative to the direction of tape travel in order to come into alignment with particular tracks. An alternative approach, also shown in FIG. 2 and enabling compatibility with both the longitudinal tracks 12A, 12B and 12C of the FIG. 1 example, and the azimuth tracks 16A and 16B of the FIG. 2 example, calls for rotating a head 19 having perpendicular head elements 19A and 19B between the two azimuth formats and the longitudinal format. One example of a multi-element head is given in commonly assigned, U.S. patent application Ser. No. 08/760,794 filed on Dec. 4, 1996, and entitled: xe2x80x9cFour Channel Azimuth and Two Channel Non-Azimuth Read-After-Write Longitudinal Magnetic Headxe2x80x9d, the disclosure thereof being incorporated herein by reference. An example of an azimuth tape recording pattern and an apparatus for writing the pattern in accordance with servo information read back from an adjacent track is given in commonly assigned U.S. Pat. No. 5,371,638, the disclosure thereof being incorporated by reference.
FIG. 3 illustrates a newer track format plan employing a tape 10A carrying high recording density magnetic media. According to the FIG. 3 track plan, a multiplicity of data tracks 20n are distributed across e.g. five zones 22A, 22B, 22C, 22D and 22E. A monolithic thin film head element 24 within the head assembly includes e.g. 12 write-read elements in relatively close proximity enabling writing to and reading from tracks of a particular zone, e.g. zone 22D in the FIG. 3 example. Other zones may be accessed by displacing the head assembly laterally relative to the direction of travel of tape 10A. Further details of a tape and tape drive in accordance with this general approach may be found in the above-referenced U.S. patent application Ser. No. 09/046,723.
While the standardized longitudinal recording patterns shown in the FIG. 1 example, and the azimuth recording patterns shown in the FIG. 2 example, have worked very well for a number of years, newer higher density track layout patterns and plans, enabled by multi-element thin film head as well as improvements in tape media technologies are now proposed and will most likely become standard approaches in the future for certain categories of longitudinal digital tape recording methods and devices. Since extensive cartridge handling equipment in use is capable of handling standard cartridges containing tape having the newer format, no compelling need has arisen to change the cartridge form factor or major features in order to accommodate the new tape track formats enabled by emerging new technologies. Yet, a hitherto unsolved need has remained for backward compatibility within tape drive units having monolithic multi-element heads by enabling reading back of older preexisting tape formats recorded on tape carried in standard tape cartridges, but based on discrete head elements, in order to recover archival data recorded on the older tapes.
A general object of the present invention is to provide a backward compatible head and head positioning assembly within a linear digital tape drive in a manner overcoming limitations and drawbacks of prior approaches. Another object of the present invention is to enable a linear digital tape drive primarily adapted to recording and reading back of track patterns of standard cartridge tape recorded in a higher density track format to also be able to read back older lower density track patterns of archival standard cartridge tape in order to be able to retrieve archived user data.
Yet another object of the present invention is to provide a secondary head positioning and read-only tape head module for backward compatibility in reading tape recorded in a low density format and carried in standard tape cartridges as well as to provide a primary head positioning and write-read tape head module for forward compatibility in reading tape recorded in a high density format and carried in the same type of standard tape cartridges.
One more object of the present invention is to provide a xe2x80x9cbutton-shapedxe2x80x9d multi-element magnetic recording head which is capable of contacting a magnetic tape at a very slight tape wrap angle, and which may be rotated between positions aligning a magnetic recording gap of an element of the head with both longitudinal and azimuthal recording patterns of a lineal data track recorded on the tape.
One more object of the present invention is to provide a tape head having side wings and dimensions less than tape width such that the tape head floats in close proximity to a tape with minimized contact, ensuring effective operation with both longitudinal and azimuthal recording patterns as well as minimal wear and reliable long useful life.
Accordingly, a tape recording and playback unit is provided for recording and playing back digital data recorded along a multiplicity of parallel longitudinal data tracks of a magnetic storage tape. The tracks are arranged in accordance with a standardized high density track layout in which the tracks have much smaller track widths and are much more closely spaced together than tracks defined by older lower density standard tape track formats. The unit includes a base, and has a take-up reel. In one preferred form, the unit receives a single reel cartridge and couples to an outer end of a tape supply held on a supply reel of the cartridge and threads the tape along a tape path defined by plural guide rollers within the unit until the take-up reel is reached.
In order to write to and read from tape tracks in accordance with the standardized high density track layout, the unit is equipped with a primary head positioning mechanism. The primary mechanism is referenced to the base and presents a multi-channel primary write/read head assembly to the tape along the tape path. A coarse servo, preferably including a lead screw and nut follower provides coarse elevational control to the primary write/read head assembly. A fine position servo, preferably including a voice coil motor carried on a body of the nut follower provides fine adjustments to head position in accordance with position error signals. Most preferably, the position error signals are provided via an optical sensor reading optical servo patterns formed on a back side of the high density tape.
In order to provide backward compatibility with lower density standard tape track layouts, a secondary head positioning mechanism is also provided within the unit. The secondary head positioning mechanism supports and positions a read-only secondary head assembly relative to the tape. The secondary head positioning mechanism also preferably includes a coarse positioner for elevational positioning. In one preferred form, the secondary head positioning mechanism also includes a mechanism for rotating the head to enable read back of longitudinal recording, azimuth recording, and to assume a retract position when a tape recorded with a lower density standard track pattern is not present. Most preferably, the coarse positioner of the secondary mechanism is mechanically coupled to the coarse positioner of the primary mechanism, in order to eliminate a second coarse positioner motor. Coupling via spur gearing between the two mechanisms is presently preferred. The electronics of the unit may be switched between the primary mechanism and the secondary mechanism, based upon sensing a particular track format standard type. In one preferred form, format sensing is by way of a unique structural feature provided on an otherwise standard tape cartridge, such that the feature distinguishes between high density and low density tape track standard formats.
A secondary read-only head body has a dimension less than a width of the tape and employs a minimized tape wrap angle. The head body has side wings enabling the head to xe2x80x9cfloatxe2x80x9d adjacent to the tape at the minimum wrap angle and effectively operate at longitudinal as well as azimuth play back angles.
These and other objects, advantages, aspects, and features of the present invention will be more fully appreciated and understood upon consideration of the following detailed description of preferred embodiments presented in conjunction with the accompanying drawings.